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Aviation History
1946
1946 - 0351.PDF
FEBRUARY 21ST, 1946 FLIGHT SERIES II GOBLIN Full Details of the Latest D.H* Turbine/Jet Engine IN the issue of Flight dated November 1st, 1945, theGoblin turbine / jet engine was. introduced together withthose chiefly responsible for its design, namely, Major F. B. Halford and Messrs. J. L. P. Brodie and E. S. Moult.The layout of the Goblin, and its descent from early Whittle designs, was at that time described, and the shipping ofunite to America for the Shooting Star was also recorded. It is now permissible to describe in detail the constructionof the Goblin II and to give the full performance figures and running conditions. When the design was first considered in 1941, one of the,most important considerations was the time element. A turbine/jet engine was needed quickly, and anything likelyto prolong the development, or unduly complicate the manufacture, had to be avoided. Under different circum-stances, an axial-flow compressor and a single annular combustion chamber might have been developed for the 2,600 2400 2200 5OO 2O.OOO' ALTITUDE 4O.OOO" 5O.OOO 20,000' ALTITUDE. The variation of thrust with altitude, at500 m.p.h. The variation of fuel consumption withaltitude, at 500 m.p.h. first D.H. unit. However, both of these, while theoreticallysuperior, were in the nature of unknown quantities, lacking in practical data and, in addition, there was already somefoundation for the belief that axial-flow compressors were proving something of a headache to German manufacturers.With regard to combustion research, a similar position existed ; a fair amount was known about small individualcombustion chambers but practically nothing of the single, large annular type. As a result, ideas for the truly'' straight-through'' design were for the time being set aside, and components were selected of a type for whichpractical performance figures would be available, namely, radially arranged combustion chambers of the accepted typeand a compressor impeller basically similar to that for, say, a piston-engine supercharger. One of the principal differences between the Goblin Seriesand other units is, of course, the use of a single-sided impeller for the centrifugal com-pressor. While it was fully realised that a double-sided impeller, asfavoured by Whittle, appeared to make possible a unit with smalleroverall diameter, and that a large- diameter impeller, besides beingmore limited in rotational speed, would raise some problems inmanufacture, the D.H. design staff felt that there was a balance infavour of the single-sided design. Direct Air Intake In particular, the greatest p0S.sible use could be made of an unin- terrupted direct air flow to the eyeof the impeller through a large intake. Ram effect could be em-ployed to the full, and eddy and friction losses were likely to bevery small. In addition, it was felt that whilea double-sided impeller made pos- sible a compressor of smaller dia-meter for a given capacity, this ad- vantage was to a great extent off-set by the need to provide annular air passages around the outside ofthe compressor between combustion chambers, for the supply of air tothe rearward-facing intake, and by the resulting less compact arrange-ment of the combustion chambers. It was also argued that the rear in-take itself, with a 180-degree turn in the air flow, seemed likely to 40,000' 50,000
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